Glycol aldehyde and ethylene glycol processes

ABSTRACT

A process for preparing glycol aldehyde by reacting formaldehyde, hydrogen and carbon monoxide at elevated temperature and superatmospheric pressure in the presence of rhodium catalyst and conversion thereof to ethylene glycol as the substantially exclusive polyol product.

This application is a continuation-in-part of U.S. application Ser. No.724,126, filed Sept. 17, 1976 and now abandoned.

This invention is concerned with processes for the preparation of glycolaldehyde, and conversion thereof to ethylene glycol, by reaction offormaldehyde, carbon monoxide and hydrogen in the presence of a rhodiumcatalyst.

Ethylene glycol is a very valuable commercial chemical with a widevariety of uses including use as a coolant and anti-freeze, monomer forpolyester production, solvent, and an intermediate for production ofcommercial chemicals.

Glycol aldehyde is a valuable intermediate in organic synthesis,including the preparation of serine, and is particularly useful as anintermediate in the production of ethylene glycol by catalytichydrogenation.

The reaction of formaldehyde with carbon monoxide and hydrogen is aknown reaction and yields, inter alia, ethylene glycol, methanol, andhigher polyhydroxy compounds. For example, U.S. Pat. No. 2,451,333describes the reaction of formaldehyde, carbon monoxide and hydrogenover a cobalt catalyst to produce mixtures of polyhydroxy compoundswhich include ethylene glycol, glycerol, and higher polyols. Variousmetal catalysts are also disclosed including nickel, manganese, iron,chromium, copper, platinum, molybdenum, palladium, zinc, cadmium,ruthenium and compounds thereof.

U.S. Pat. No. 3,920,753 describes the production of glycol aldehyde byreaction of formaldehyde with carbon monoxide and hydrogen in thepresence of a cobalt catalyst under controlled reaction conditions, butwith comparatively low yields.

Polyols are also produced by reaction of carbon monoxide and hydrogenover various metal catalysts. U.S. Pat. No. 3,833,634 describes thisreaction catalyzed by rhodium to produce ethylene glycol, propyleneglycol, glycerol, methanol, ethanol, methyl acetate, etc. Rhodiumcatalysts are also employed in the production of oxygenated derivativesof alkenes, alkadienes and alkenoic acid ester by reaction with carbonmonoxide and hydrogen, as described, for example, in U.S. Pat. Nos.3,081,357; 3,527,809; 3,544,635; 3,557,219; and 3,917,661.

The prior art processes for production of ethylene glycol havecharacteristically provided mixtures of products, the principalco-products being propylene glycol and glycerine, along with the loweralcohols, methyl and ethyl alcohol. Thus, these processes are encumberedby the need for expensive and time-consuming separation techniques whereethylene glycol is the desired product. In addition, the efficiency ofthe reaction in terms of yield of ethylene glycol is not high due to theconcomitant formation of the co-products, which are usually present insignificant amounts.

It has now been found that the reaction of formaldehyde, carbon monoxideand hydrogen over rhodium catalyst appears to involve a two-stagereaction, with the first stage yielding glycol aldehyde and methanol,and the second stage yielding ethylene glycol. Thus, this reaction isanalogous to that realized with cobalt catalysts as collectivelydisclosed in the aforementioned U.S. Pat. Nos. 2,451,333 and 3,920,753,the surprising difference residing in the high selectivity of thepresent inventive process which exclusively leads to ethylene glycol asthe sole detectable polyol obtained in the second stage of the reaction.Further, the conversion to glycol aldehyde realized in the first stageof the present process is substantially greater than that obtained inthe process described in U.S. Pat. No. 3,920,753.

Thus, in the preferred forms of the invention, the present processprovides glycol aldehyde in substantially higher yield than heretoforeattainable from formaldehyde, carbon monoxide and hydrogen, providesethylene glycol as the exclusive, detectable polyol product, in improvedyields when compared to similar processes.

The very desirable results obtained in accordance with the presentprocess renders the process particularly amenable to commercialproduction of ethylene glycol, not only from the viewpoint of attainablehigh yields of ethylene glycol, but also the ease of recovery ofethylene glycol from the co-produced methanol, e.g., by simplefractional distillation. The ease of recovery is extremely importantsince it permits separation of the ethylene glycol from the productmixture even in those process runs where methanol may be produced as themajor product, the glycol being the minor product. Thus, even where theglycol is present in amounts corresponding to about 10 mole-percent, andeven less, of the reaction product mixture, the ease of separation willpermit recovery of the glycol.

Glycol aldehyde is also produced in a high order of purity. Usually, thefirst stage reaction mixture can be used as such in the second stagereaction mixture can be used as such in the second stage to produceethylene glycol by reduction of glycol aldehyde to obtain the glycol asthe sole polyol product.

It is, of course, axiomatic that prior art procedures are seriouslyencumbered by the fact that the reaction product is a mixture of polyols(including ethylene glycol) which are extremely difficult to separateeven when employing multiple fractional distillations.

The process of the present invention is accomplished by contactingformaldehyde, carbon monoxide and hydrogen, preferably in a suitablesolvent, in the presence of a rhodium-containing catalyst at elevatedtemperature and superatmospheric pressure. The major product of the twostage reaction is ethylene glycol, with the major by-product beingmethanol. The manner of contact is not critical since any of the variousprocedures normally employed in this type of reaction can be used aslong as efficient gas-liquid contact is provided. Thus, the process maybe carried out by contacting a solution of formaldehyde together withthe rhodium catalyst with a mixture of carbon monoxide and hydrogen atthe selected conditions. Alternatively, the solution of formaldehyde maybe passed over the catalyst in a trickle phase under a mixture of carbonmonoxide and hydrogen at the selected conditions of temperature andpressure.

In view of the two-stage nature of the present process to produceethylene glycol, the implementation can take several forms. The reactioncan be accomplished by allowing both stages to proceed consecutively atsuitable temperature and pressure, or alternatively the reaction can bestopped at the end of the first phase where the product is glycolaldehyde and the second phase can be carried out under any applicablereduction process which will result in conversion of the aldehyde groupof glycol aldehyde to a primary alcohol group resulting in ethyleneglycol.

A wide variety of reduction processes can be employed for the secondphase reaction including the well-known chemical reducing agentsemployed in reducing aldehydes to primary alcohols. For commercialprocesses, however, where possible, catalytic reductions employinghydrogen are usually preferred since they are more practical andefficient especially with catalysts which can be regenerated and thusare re-usable. In the present process, catalytic hydrogenation ispreferred for the same reasons, especially with catalysts which can beregenerated. Any hydrogenation catalyst can be employed.

Thus, typical hydrogenation catalysts include, for example, RaneyNickel, cobalt, copper chromite, rhodium, palladium, platinum, andsimilar such metal catalysts, which can be used conveniently on supportssuch as charcoal silica, alumina, kieselguhr and the like. Theconditions of catalytic hydrogenation are well-known and, in general,the reaction can be conducted at temperatures ranging from about 30° toabout 150° C., usually at pressures of from about 100 to about 5000psig. The use of higher temperatures and pressures, though operable,provides no special advantage and usually requires special equipmentwhich economically is disadvantageous and therefore not preferred.

Particularly preferred catalysts are those which characteristicallyrequire short reaction times, e.g. palladium and nickel, which is mostdesirable for commercial processes for economic reasons.

As mentioned hereinbefore, the main product of the first stage reactionis glycol aldehyde, along with methanol. Glycol aldehyde tends to formacetals, a reaction typical of aldehydes, and in view of the primaryalcohol group present in the molecule, this compound forms hemi-acetalsand acetals with itself in the form of, for example, linear and cyclicacetals, represented by the formulas: ##STR1## In addition, glycolaldehyde forms acetals and hemiacetals with methanol, and, if present,ethylene glycol. Acetals in particular are resistant to hydrogenationand should preferably be hydrolyzed to the free aldehyde so thatefficient reduction to ethylene glycol can be effected.

The hydrolysis reaction can be accomplished merely by assuring thepresence of water in the reaction mixture, preferably in at leastequivalent molar quantities. Thus, equimolar amounts of water arerequired to assure complete hydrolysis, with less than equimolarresulting in less than complete hydrolysis of the acetal present in themixture which, in turn, results in lower yield of ethylene glycol. It isconvenient to hydrolyze the acetal immediately prior to and/orconcurrent with the reduction stage.

Oftentimes, the amount of water required for substantial hydrolysis ofthe aforementioned acetals may already be present in the first stagereaction which ideally contains small amounts of water for best results,e.g. from about 0.5 to about 10% by volume. Alternatively, whereinsufficient water is present, the necessary water level can be achievedby mere addition of water to the second stage reaction, either batchwiseor by metering over the course of the reaction. In experience to thepresent time, optimum final levels of water are in the range of fromabout 10-30% by volume based on the hydrogenation mixture.

To facilitate hydrolysis, the presence of an acid is particularlydesirable. Thus, strong mineral acids, such as hydrohalic acids,sulfuric, and phosphoric acids or, preferably, weak organic acids,especially lower alkanoic acids such as acetic and propionic acids, canbe employed for this purpose. Strong mineral acids should be avoidedwhere the reaction solvent is reactive therewith, e.g. amide solventswhich hydrolyze. As will be apparent from the following disclosure,amide solvents are usually preferred, particularly in the first stagereaction and with these solvents, it is preferred to employ weak acidsto catalyze the acetal hydrolysis. The amount of acid employed does notappear to be critical and even trace amounts are effective, as should beobvious to those skilled in this art.

Thus, it is apparent that a separate hydrolysis step is not alwaysnecessary since the normal water content of the first stage reactionwill hydrolyze at least part of the acetals produced and the hydrolyzedpart will reduce to ethylene glycol. However, maximizing yield ofethylene glycol dictates the inclusion of a hydrolysis step to assuremaximum hydrolysis and thus the highest realizable yield of ethyleneglycol. Accordingly, the inclusion of the hydrolysis step, though notalways essential, amounts to good technique, which, in view of thesimplicity of adding water, with or without acid present, is readilypracticable.

The combined hydrolysis-hydrogenation step can be carried out byart-recognized techniques as described, for example, in U.S. Pat. Nos.4,024,197; 2,721,223; 2,888,492 and 3,729,650 incorporated herein byreference for the disclosed combined reactions.

The catalyst for the first stage reaction may be elemental rhodium, or arhodium compound, complex or salt, or mixtures thereof, employed as suchor deposited or affixed to a solid support such as molecular sievezeolites, alumina, silica, anion exchange resin or a polymeric ligand.In the active form, the catalyst comprises rhodium in complexcombination with carbon monoxide, i.e., rhodium carbonyl, which maycontain additional ligands as described, for example, in U.S. Pat. No.3,527,809 and the aforementioned U.S. Pat. No. 3,833,634, each of whichis incorporated herein by reference for the disclosure of rhodiumcomplexes containing carbon monoxide and organic ligands as well ashydrogen as a ligand. As described in U.S. Pat. No. 3,833,634, suitableorganic ligands are compounds which contain at least one nitrogen and/orat least one oxygen atom, said atoms having a pair of electronsavailable for formation of coordinate bonds with rhodium. Illustrativeorganic ligands include various piperazines, dipyridyls, N-substituteddiamines, aminopyridines, glycolic acid, alkoxy-substituted aceticacids; tetrahydrofuran, dioxane, 1,2-dimethoxybenzene, alkyl ethers ofalkylene glycols, alkanolamines, iminodiacetic acid, nitrilotriaceticacid, ethylenediaminetetraacetic acid, and the like. In U.S. Pat. No.3,527,809 are described phosphorus-containing ligands such as trialkyl,triaryl and tricycloalkyl phosphites and triarylphosphines, as well asthe analogous antimony and arsenic compounds.

Especially preferred catalysts are those including phosphines as ligand,particularly triaryl phosphines, such as triphenyl phosphine.Illustrative catalysts are well-known and described in the scientificliterature. Most preferred of such catalysts are those which includehalide, preferably chloride, which result in higher yield of glycolaldehyde in shorter reaction times than correspondingnonchloride-containing catalysts.

The phosphine-containing catalysts can be prepared by the methodsdescribed in the aforesaid U.S. Pat. No. 3,527,809 employing suitableligands exemplified as follows:

    ______________________________________                                        Trimethylphosphine                                                                              Ethyl-bis(beta-phenylethyl)                                                   phosphine                                                   Triethylphosphine Tricyclopentylphosphine                                     Tri-n-butylphosphine                                                                            Tricyclohexylphosphine                                      Triamylphosphines Dimethyl-cyclopentylphosphine                               Trihexylphosphines                                                                              Tri-octylphosphine                                          Tripropylphosphine                                                                              Dicyclohexylmethylphosphine                                 Trinonylphosphines                                                                              Phenyldiethylphosphine                                      Tridecylphosphines                                                                              Dicyclohexylphenylphosphine                                 Triethylhexylphosphine                                                                          Diphenyl-methylphosphine                                    Di-n-butyl octadecylphosphine                                                                   Diphenyl-butylphosphine                                     Dimethyl-ethylphosphine                                                                         Diphenyl-benzylphosphine                                    Diamylethylphosphine                                                                            Trilaurylphosphine                                          Tris(dimethylphenyl)phosphine                                                                   Triphenylphosphine                                          ______________________________________                                    

Using this procedure, preferred catalysts can be prepared by selectionof suitable ligands and rhodium compounds, including the following:

RhCl(CO)(PPh₃)₂

RhCl(PPh₃)₃

RhBr(CO)(PPh₃)₂

RhI(CO)(PPh₃)₂

RhCl(CO)(PEt₃)₂

RhCl(CO)[P(p-MeC₆ H₄)₃ ]₂

RhCl(CO)[P(p-MeOC₆ H₄)₃ ]₂

RhCl(CO)[P(p-FC₆ H₄)₃ ]₂

RhCl₃ (CO)(PPh₃)₂

RhCl₃ (PEt₂ Ph)₃

Rh(CO)H(PPh₃)₃

RhCl(CO)(PEt₂ Ph)₂

The catalyst can be employed in soluble form or in suspension in thereaction medium, or alternatively deposited on porous supports. Thecatalyst can be prepared by various techniques. For example, the complexwith carbon monoxide can be preformed and then introduced into thereaction medium, or, alternatively, the catalyst can be formed in situby reaction of rhodium, or rhodium compound, directly with carbonmonoxide which may be effected in the presence of a selected orgnanicligand to form the organic ligand-carbon monoxide-rhodium complexes inthe reaction medium.

When glycol aldehyde is the desired product, of course, only the firststage reaction need be carried out. The product obtained is usually inthe form of the aforementioned acetals and can be separated from thecoproduced methanol and reaction solvent, if necessary, by fractionaldistillation. Gas chromatography and mass spectrophotometric analysisare used to identify the product as glycol aldehyde. In addition, thedimedone (5,5-dimethylcyclohexand-1,3-dione) derivative of pure glycolaldehyde was prepared and compared with the dimedone derivative of theproduct obtained from the typical reaction according to the presentprocess to show them to be identical. NMR analysis of the derivativeconfirmed glycol aldehyde as the product. No glyoxal was detected by anyof the aforementioned analytical techniques.

The first stage reaction which results in glycol aldehyde, and methanol,production is usually substantially complete in relatively shortreaction times, usually less than about one hour, with substantial yieldof product realized in as little as 30 minutes, and even less time.Usually, only small amounts of ethylene glycol, if any, can be detected.

As should be apparent, the rhodium catalyst employed in the first stagereaction can also serve as the hydrogenation catalyst for the secondstage reaction to produce ethylene glycol. Thus, if the first phasereaction is allowed to continue, eventually the hydrogenation reactionwill yield ethylene glycol. Particularly excellent yields are obtainedby adding water, where necessary, to hydrolyze the glycol aldehydeacetals present from the first stage reaction thus realizing maximumyields of ethylene glycol. In general, the rhodium catalyst of the firststage reaction is an effective catalyst for the second stagehydrogenation, but does not provide as short reaction times as can berealized with other hydrogenation catalysts, under the usual reactionconditions.

To shorten the second stage reaction time, it is possible to effect thereduction step over metal catalysts such as palladium and nickel, and itis usually preferred to effect the second stage reaction in a separatereactor. Thus, the first stage reaction can be conducted in a firstreactor under selected conditions of temperature and pressure, and aftercompletion the first stage product, with or without isolation from thereaction mixture, can then be transferred to a second reactor underselected conditions of temperature and pressure to effect thehydrogenation reaction under hydrolysis conditions, i.e., in thepresence of at least the stoichiometric amount of water to hydrolyze theglycol aldehyde acetals present.

Alternatively, the two stage reaction can be conducted in one reactorwith provision for controlling the reaction parameters. At the time ofthe hydrogenation stage, the selected hydrogenation catalyst can beadded, conveniently with the water required for hydrolysis, if any isneeded, and the hydrogenation reaction can then proceed. In this lattermodification, the hydrogenation catalyst can be added to the first phasereaction mixture with or without the first phase rhodium catalyst beingpresent. Generally, it is preferred to remove the rhodium catalyst,particularly if this can be done conveniently so that competitivecatalysis will not impede the hydrogenation reaction, and, moreimportantly, to permit more accurate control over the reaction.

The present invention, therefore, provides a simplified process forselective production of glycol aldehyde as the sole detectable aldehydeproduct. In addition, this invention affords a simplified process forobtaining ethylene glycol by either allowing the initial process forglycol aldehyde to continue so that hydrogenation under hydrolyticconditions yields ethylene glycol or, alternatively, the glycol aldehydeproduct of the first stage reaction is reduced under hydrolyticconditions employing art-recognized reduction processes to ethyleneglycol. In the latter process, the glycol aldehyde product of the firststage reaction can be used in the form of the reaction mixture, or theproduct can be isolated, as by fractionation, and used in purified form.

The amount of catalyst employed in the first stage reaction does notseem to be critical and can vary considerably. At least a catalyticallyeffective amount of catalyst should be used, of course. In general, anamount of catalyst which is effective to provide a reasonable reactionrate is sufficient. As little as 0.001 gram atoms of rhodium per literof reaction medium can suffice while amounts in excess of 0.1 gram atomsdo not appear to materially affect the rate of reaction. For mostpurposes, the effective preferred amount of catalyst is in the range offrom about 0.002 to about 0.025 gram atoms per liter.

The reaction conditions are not overly critical in that wide ranges ofelevated temperature and superatmospheric pressures are operable. Thepractical limitations of production equipment will dictate to a greatextent the selection of temperatures and pressure at which the reactionis to be effected. Thus, using available production systems, theselected elevated temperature should be at least about 75° C. and canrange up to about 250° C. and even higher. For most purposes, thepreferred operating temperature ranges from about 100° to about 175° C.The superatmospheric pressure should be at least about 10 atmospheresand can range up to almost any pressure attainable with productionapparatus. Since extremely high pressure apparatus is quite expensive,pressures to about 700 atmospheres are suggested. Most desirably, thepressure should be in the range of from about 150 to about 400atmospheres, particularly when employing the aforesaid preferredtemperature range.

The reaction is preferably carried out in a solvent which will dissolvepolar materials and which preferably is aprotic in order to maximizeselectively to ethylene glycol. Suitable solvents include a wide varietyand are exemplified by N-substituted amides in which each hydrogen ofthe amido nitrogen is substituted by a hydrocarbon group, e.g.,1-methylpyrrolidin-2-one, N,N-dimethylacetamide, N,N-diethylacetamide,N-methylpiperidone, 1,5-dimethylpyrrolidin-2-one,1-benzylpyrrolidin-2-one, N,N-dimethylpropionamide, hexamethylphosphorictriamide and similar such liquid amides; nitriles, such as acetonitrile,benzonitrile, propionitrile and the like; cyclic ethers such astetrahydrofuran, dioxane and tetrahydropyran; ethers such as diethylether, 1,2-dimethoxybenzene, alkyl ethers of alkylene glycols andpolyalkylene glycols, e.g., methyl ethers of ethylene glycol, propyleneglycol and di-, tri- and tetraethylene glycols; ketones such as acetone,methyl isobutyl ketone, and cyclohexanone; esters, such as ethylacetate, ethyl propionate and methyl laurate; lactones of organiccarboxylic acids such as butyrolactone and valerolactone organic acidssuch as acetic acid, propionic acid and caproic acid; and alkanols, suchas methanol, ethanol, propanol, 2-ethylhexanol and the like; andmixtures thereof. Many of the solvents are non-reactive in the mediumwhereas others are capable of functioning as ligands. The selectedsolvent should preferably be liquid under the reaction conditions.

When employed, solvents appear to exert varying influences on the yieldof product formed and the selectivity to ethylene glycol, depending onthe nature of the solvent. For example, when lower alkanoic acids, e.g.,acetic acid, are present for example as a co-solvent in the first stagereaction the reaction appears to proceed more rapidly but the yield ofglycol decreases somewhat while that of methanol increases. When aceticacid was employed at a level of from about 10 to about 20 volume percentof the reaction mixture, the reaction proceeded in about one-half thetime required for the same solvent containing no acetic acid but withincreased methanol production (55% vs. 40%) and decreased glycolproduction (30% vs. 48%). Further, basic amines such as pyridine,triethylamine and amines of comparable basicity appear to exert anegative influence on the yield of glycol aldehyde obtained and thisinfluence becomes more pronounced as the molar ratio of amine to rhodiumincreases. Thus, even when the amine is present as a co-solvent, thetendency is towards reduced yield of glycol aldehyde when compared tosolvent systems from which amines are excluded. Protic solvents such aswater, phenols and carboxylic acids, e.g., acetic acid, in largequantities, e.g. greater than about 30-40% by volume, exert a similarnegative influence on the yield of glycol aldehyde. In most cases, thedecrease in yield of glycol aldehyde is accompanied by an increase inmethanol yield, while in some cases the conversion of formaldehyde isreduced so that the yield of both products is reduced. Thus, whereoptimum yields of glycol aldehyde and ethylene glycol and minimum yieldsof methanol are desired, basic amines or protic solvents in significantamounts are usually avoided, particularly in the first stage reaction.

On the other hand, certain solvent systems favor high selectivity forglycol aldehyde and ethylene glycol production, and in many casessubstantially lower yields of methanol are obtained. Solvents such asorganic amides, in particular, favor high selectivity for glycolaldehyde and ethylene glycol production, and in many cases substantiallylower yields of methanol are obtained, for which reason these solventsare preferred. Hydrocarbon solvents can be employed but apparentlyresult in lower yields of glycol aldehyde and glycol than obtained withthe preferred solvents.

The preferred solvents are aprotic organic amides. The contemplatedamides include cyclic amides, i.e. in which the amino group is part of aring structure such as in pyrrolidinones and piperidones; acylatedcyclic amines, such as N-acyl piperidines, pyrroles, pyrrolidines,piperazines, morpholines, and the like, preferably in which the acylgroup is derived from a lower alkanoic acid, e.g. acetic acid; as wellas acyclic amides, i.e., wherein the amido group is not part of a ringstructure as in acetamides, formamides, propionamides, caproamides andthe like. The most preferred of the amides are those in which the amidohydrogen atom are fully replaced by hydrocarbon groups preferablycontaining not more than 8 carbon atoms. Exemplary hydrocarbon groupsare alkyl, preferably lower alkyl such as methyl, ethyl and butyl;aralkyl, such as benzyl and phenethyl; cycloalkyl, such as cyclopentyland cyclohexyl; and alkenyl, such as allyl and pentenyl. The preferredamido nitrogen substituents are lower alkyl, especially methyl, ethyland propyl groups and aralkyl groups, especially benzyl. The mostpreferred amide solvents include 1-methylpyrrolidin-2-one,1-ethylpyrrolidin-2-one, 1-benzylpyrrolidin-2-one, N,N-diethylacetamide,and N,N-diethylpropionamide.

The nitrile solvents include any organic nitrile solvent preferablycontaining up to about 8 carbon atoms, such as acetonitrile,benzonitrile, phenylacetonitrile, capronitrile and the like. Mixtures ofsolvents can be employed.

The reaction pressures represent the total pressure of the gasescontained in the reactor, i.e., carbon monoxide and H₂, and, if present,any inert diluent gas such as nitrogen. As in any gaseous system, thetotal pressure is the sum of partial pressures of component gases. Inthe present reaction, the molar ratio of hydrogen to carbon monoxide canrange from about 1/10 to about 10/1, with the preferred ratio, fromabout 1/5 to about 5/1, and the reaction pressure can be achieved byadjusting the pressure of these gases in the reactor.

For best results, the molar ratio of carbon monoxide to hydrogen ismaintained at high values in the first stage reaction where high partialpressures of carbon monoxide favor production of glycol aldehyde. In thesecond stage reaction, high partial pressure of hydrogen is desirablefor reduction reaction. Thus, in the first stage reaction to produceglycol aldehyde, the partial pressure of carbon monoxide is usuallyadjusted to be about 3 to about 10 times that of hydrogen. In the secondstage reaction, i.e. the hydrogenation, the partial pressure of hydrogenis adjusted to a high value to facilitate the reaction. Such adjustmentof the gas feed can be readily accomplished. For example, after thefirst phase reaction is substantially complete, the reactor need only bebled to lower the pressure and then pressurized with hydrogen gas toachieve the desired high partial pressure of hydrogen. Carbon monoxidepresent in the gaseous system of the first phase reaction need not becompletely purged from the reactor prior to repressurizing with hydrogengas. Of course, carbon monoxide can reduce the efficiency of certaincatalyst systems, possibly through poisoning as is known, and preferablyis excluded when such systems are employed.

Where the second phase reaction is carried out in a separate reactorwhether over the originally present rhodium catalyst or a differentmetal hydrogenation catalyst, the reaction is normally conducted underhydrogen gas without diluent gas, as is usual in catalyzed hydrogenationreactions.

The source of formaldehyde for the present process can be any of thosecommonly used in this technology including paraformaldehyde, methylal,formalin solutions, and polyoxymethylenes. Of these, paraformaldehyde ispreferred since best yields are attained therewith. Solutions offormaldehyde in solvents, advantageously the reaction solvent, can beused, e.g. solutions of formaldehyde in aqueous reaction solvent, suchas N-methyl pyrrolidin-2-one. The use of methylal may be attended by areduction in yield of ethylene glycol. If trioxane is employed, becauseof its stability, a hydrolyzing agent should be employed to releaseformaldehyde.

As with any process of this kind, the present process can be conductedin batch, semi-continuous, and continuous operation. The reactor shouldbe constructed of materials which will withstand the temperatures andpressures required, and the internal surfaces of the reactor aresubstantially inert. The usual controls can be provided to permitcontrol of the reaction such as heat-exchangers and the like. Thereactor should be provided with adequate means for agitating thereaction mixture; mixing can be induced by vibration, shaking, stirring,oscillation and like methods. Catalyst as well as reactants may beintroduced into the first stage or the second stage reactor at any timeduring the process for replenishment. Recovered catalyst, solvent andunreacted starting materials may be recycled.

The relative yields of ethylene glycol and methanol are not overlycritical since the product mixture can be readily separated into thecomponents by known techniques, especially by fractional distillation,regardless of the proportions contained in the mixture. Therefore, evenwhere ethylene glycol is 10-20% of the reaction mixture, it can bereadily separated from the mixture, especially in continuous processproduction of ethylene glycol, with the methanol recycled asformaldehyde. Of course, the preferred processes yield mixtures in whichethylene glycol predominates as the reaction product.

In addition to the aforementioned solvent effects, other factors alsoaffect the yields of ethylene glycol and methanol and the conversion offormaldehyde in the process. For example, in the combined two-stagereaction, the use of low partial pressures of carbon monoxide appears tofavor greater methanol production, whereas the use of high partialpressure of CO, particularly during the first stage, results in lowermethanol yields without significant change in glycol yield. Thus, at apartial pressure of carbon monoxide at 1900 psig., the conversion offormaldehyde amounted to 57% with a 76% molar selectivity for ethyleneglycol whereas at 1055 psig., the conversion was 72% and molarselectivity was 56% under otherwise identical conditions. Increasedpartial pressure of hydrogen particularly in the combined reactionresulted in increased glycol selectivity and increased conversion offormaldehyde with little, if any, change in methanol yield.

The effect of temperature variations in the preferred temperature rangeis not as pronounced, with higher formaldehyde conversion and ethyleneglycol selectivity being obtained in the 100°-175° C. range,particularly during the first stage reaction.

The process conditions for the separate first stage reaction areessentially the same as employed in the first stage of the combinedtwo-stage reaction. Thus, the reaction is carried out at a temperatureof at least about 100° C. to obtain a reasonable reaction rate althoughsomewhat lower temperatures can be employed with slower reaction ratesbeing realized. For reaction times of about one hour, and even less, thetemperature should be in the range of from about 100° C. to about 175°C., preferably from about 120° to about 160° C. As in the combined twostage reaction, the partial pressure of carbon monoxide is preferablyhigh, in comparison to that of hydrogen, with the preferred ratios beingfrom about 2:1 to about 10:1, the more preferred being from about 3:1 toabout 8:1. The total pressure of gas used is generally maintained atfrom about 1000 psi up to about 9000 psi, with from about 3000 to about7000 psi being preferred. Of course, higher pressures and highertemperatures can be used but with no appreciable advantage and, sincethey require the use of special high pressure equipment, they areusually avoided.

The reaction conditions employed in the second stage reaction, i.e., thehydrogenation, can be any of the standard reaction temperatures andpressures employed for such reactions since neither temperature norpressure are critical for this reaction. Preferably, the hydrogenationis conducted at a temperature of at least about 100° C. in order toeffect a reasonable reaction rate. Of course, lower temperatures can beused if longer reaction times can be tolerated. The pressure of hydrogengas is not excessively critical as long as sufficient gas is availablefor the hydrogenation. For convenience, the pressure will range fromabout 500 psi to as much as 5000 psi, although even higher pressures canbe employed.

When the catalyst selected for the hydrogenation step is other thanrhodium, it is preferred to remove the rhodium catalyst from the firststage reaction mixture. This preference is primarily predicated on thedesirability of avoiding concomitant catalytic effects which may tend toreduce the yield of ethylene glycol, the desired product. It has beendetermined, for example, that the yield of ethylene glycol wasconsiderably lessened when the hydrogenation was effected over supportednickel or palladium catalyst using the first stage reaction mixturewithout removing the rhodium catalyst present therein. When thesehydrogenations were repeated with the addition of water to the reactionmixture, the water preferably containing at least catalytic amounts ofacid, usually acetic acid, almost quantitive conversion to ethyleneglycol occurred, particularly when Palladium catalyst, e.g. Pd/C, isused. However, after the glycol aldehyde is separated from rhodiumcatalyst, e.g. by distillation, the glycol aldehyde is reduced almostquantitatively with catalysts such as palladium on carbon in the absenceor presence of rhodium. The aforesaid reduced yields of ethylene glycolare explainable by the production of unidentified high boiling liquidproduct which remains after distillation of ethylene glycol from thereaction mixture. Apparently, secondary competitive reactions proceedwhere both the rhodium catalyst and the hydrogenation metal catalyst aresimultaneously present in the hydrogenation reaction mixture, the natureof which reactions is not understood up to the present. Surprisingly, nosignificant amounts of the high boiling residue were discovered in thereactions mixtures obtained with either rhodium or other metal as thesole hydrogenation catalyst. With Pd/C, glycol aldehyde is almostquantitatively reduced to ethylene glycol.

The results obtained with the present new process are surprisingly andtotally unexpected. As hereinbefore described, the prior art processesof reacting formaldehyde, carbon monoxide and hydrogen have led tomixtures of polyol products principally ethylene glycol, glycerol andhigher diols from which it is extremely difficult to separate theindividual components. The present process on the other hand,selectively yields ethylene glycol as the polyol product. Analysis ofthe product produced by means of gas-liquid chromatography has failed toreveal any polyol other than ethylene glycol, which is readily separatedfrom methanol, the monohydric alcohol product, as hereinbeforementioned.

The following examples further illustrate the invention.

EXAMPLE 1

A 71 ml. stainless steel reactor fitted with a glass liner is chargedwith 0.5 g of commercial paraformaldehyde 0.019 g Rh(CO)₂ (C₅ H₇ O₂) and5 ml. N-methylpyrrolidinone. The reactor is pressured to 4350 psig withH₂ and CO at a ratio of 2.2/1 and then shaken by a wrist action shakerin a hot air oven at 150° C. for five hours. After cooling and ventingthe gases, the reaction mixture is analyzed via gas-liquidchromatography and is found to contain 0.07 g. of methanol and 0.43 g.of ethylene glycol. No higher polyols are observed.

EXAMPLE 2

The reaction is carried out as in Example 1 except the reactor ispressured to 3350 psig and H₂ and CO at a ratio of 1.5/1. The reactionsolution is analyzed and found to contain 0.08 g. of methanol and 0.34g. of ethylene glycol. Identification of ethylene glycol is confirmed bymass spectrometry.

EXAMPLE 3

The reaction is carried out as in Example 1 except the reactor ispressured to 2350 psig with H₂ and CO at a ratio of 1.7/1. Analysisafter the reaction shows the presence of 0.07 g. of methanol and 0.25 g.of ethylene glycol.

EXAMPLE 4

The reaction is carried out as in Example 1 except that 2.5 g. ofmethylal is charged in place of paraformaldehyde and the reactor ispressured to 3330 psig. with H₂ and CO at a ratio of 1.5/1. Analysis ofthe solution after reaction shows the presence of 0.26 g. of methanoland 0.06 g. of ethylene glycol.

EXAMPLE 5

The reaction is carried out as in Example 1 except the reactor ispressurized to 3750 psig. with H₂ and CO at a ratio of 4/1. Analysis ofthe reaction mixture shows the presence of 0.16 g. of methanol and 0.40g. of ethylene glycol.

EXAMPLE 6

The reaction is carried out as in Example 2 except the formaldehyde ischarged as 1.28 g. of 37% aqueous solution stabilized with methanol.Analysis of the reaction solution shows the presence of 0.29 g. ofmethanol (after correcting for the initial methanol) and 0.25 g. ofethylene glycol.

EXAMPLE 7

The reaction is carried out as in Example 1 except the formaldehyde ischarged as 0.5 g. of alkali precipitated α-polyoxymethylene and thereactor is pressured to 3500 psig. with H₂ and CO at a ratio 2.3/1.Analysis of the reaction solution shows the presence of 0.17 g. ofmethanol and 0.30 g. of ethylene glycol.

EXAMPLE 8

The reaction is carried out as in Example 2 except the reactiontemperature is 175° C. Analysis of the reaction solution shows thepresence of 0.06 g. of methanol and 0.25 g. of ethylene glycol.

EXAMPLE 9

The reaction is carried out as in Example 2 except the reactiontemperature is 125° C. Analysis of the reaction solution shows thepresence of 0.08 g. of methanol and 0.33 g. of ethylene glycol.

EXAMPLE 10

A 71 ml. stainless steel reactor equipped with a glass liner is chargedwith 0.0037 g Rh(CO)₂ (C₅ H₇ O₂), 1.0 g. paraformaldehyde and 5 ml.N-methylpyrrolidinone, pressured to 3000 psig. with H₂ and CO in a ratioof 1.5/1, and shaken ten hours at 200° C. After cooling and venting thegases analysis of the reaction solution shows the presence of 0.51 g. ofmethanol and 0.16 g. of ethylene glycol.

EXAMPLE 11

The reaction is carried out as in Example 10 except the charge is 0.037g. Rh(CO)₂ (C₅ H₇ O₂), 1.0 g. paraformaldehyde and 5 ml. ofhexamethylphosphoric triamide, and the pressure is 3330 psig with H₂ andCO in a ratio of 1.5/1. The reaction is carried out for five hours at150° C. Analysis of the reaction solution shows the presence of 0.58 g.of methanol and 0.20 g. of ethylene glycol.

EXAMPLE 12

The reaction is carried out as in Example 11 except the solvent isN,N-dimethylacetamide. Analysis of the reaction product shows thepresence of 0.64 g. of methanol and 0.32 g. of ethylene glycol.

EXAMPLE 13

The reaction is carried out as in Example 2 except the solvent isacetonitrile. Analysis of the reaction product shows the presence of0.10 g. of methanol and 0.14 g. of ethylene glycol.

EXAMPLE 14

The reaction is carried out as in Example 2 except the solvent isN-methylpiperidone. Analysis of the reaction product shows the presenceof 0.32 g. of methanol and 0.16 g. of ethylene glycol.

EXAMPLE 15

The reaction is carried out as in Example 2 except the solvent isN-benzylpyrrolidone. Analysis of the reaction product shows the presenceof 0.28 g. of methanol and 0.09 g. of ethylene glycol.

EXAMPLE 16

The reaction is carried out as in Example 7 except the solvent isN,N-diethylacetamide and the formaldehyde is charged as 0.5 g. ofparaformaldehyde. Analysis of the reaction product shows the presence of0.05 g. of methanol and 0.29 g. of ethylene glycol.

EXAMPLE 17

The reaction is carried out as in Example 16 except the solvent is1,5-dimethyl-2-pyrrolidinone. Analysis of the reaction product shows thepresence of 0.35 g. of methanol and 0.17 g. of ethylene glycol.

EXAMPLE 18

The reaction is carried out as in Example 7 except that the formaldehydeis charged as paraformaldehyde, the solvent is 1,4-dioxane and the H₂/CO ratio is 2.0/1. Analysis of the reaction product shows the presenceof 0.07 g. of methanol and 0.16 g. of ethylene glycol.

EXAMPLE 19

The reaction is carried out as in Example 18 except the solvent isbenzonitrile. Analysis of the reaction product shows the presence of0.13 g. of methanol and 0.1 g. of ethylene glycol.

EXAMPLE 20

A 300 ml. Magne-Stir autoclave equipped with a Disperso-Max stirrerwhich was operated at 1500 rpm was charged with 0.285 g. of Rh(CO)₂ (C₅H₇ O₂), 7.5 g. of 95% paraformaldehyde and 75 ml of N-methylpyrrolidone.The reactor is closed and, while the solution is stirred, pressured to3500 psig with H₂ and CO at a 3/1 ratio. The reactor is heated to 150°C. Maximum pressure of 4650 psig is reached at 138° C. When the pressuredrops to 4100 psig, the reactor is repressured to 5000 psig with H₂ andCO at a 2/1 ratio. Total reaction time at 150° C. is 3 hours. Aftercooling and venting the reactor is opened and the product solutionrecovered. Analysis of the product shows the presence of 3.0 g. ofmethanol and 6.0 g. of ethylene glycol.

EXAMPLE 21

The procedure of Example 20 is repeated except that the autoclave ispressured to give 5000 psig at 125° C. with H₂ and CO at a ratio of1.86/1. The reactor is heated, with stirring at 1500 rpm, to 125° C.When the pressure drops to 4200 psig, the autoclave is repressured to5000 psig with the same gas mixture. The total time at 125° C. is fivehours. Analysis of the product solution shows the presence of 1.3 g. ofmethanol and 6.6 g. of ethylene glycol.

EXAMPLE 22

The reaction is carried out as in Example 21 except the H₂ and CO wereat a ratio of 1/1 and at an initial pressure of 5200 psig at 125° C.Analysis of the product solution shows the presence of 4.2 g of methanoland 2.8 g. of ethylene glycol.

EXAMPLE 23

The reaction is carried out as in Example 21 except that 0.143 g. ofRh(CO)₂ (C₅ H₇ O₂) is charged. Analysis of the product solution showsthe presence of 1.3 g. of methanol and 1.8 g. of ethylene glycol.

EXAMPLE 24

The reaction is carried out as in Example 21 except that 0.428 g. ofRh(CO)₂ (C₅ H₇ O₂) is charged and the reaction time is three hours.Analysis of the product solution shows the presence of 1.0 g. ofmethanol and 6.3 g. of ethylene glycol.

EXAMPLE 25

The reaction is carried out as in Example 1 except the catalyst ischarged as 0.008 g. powdered elemental rhodium and the temperature is250° C. Analysis of the product solution shows the presence of 0.32 g.of methanol and 0.17 g. of ethylene glycol.

EXAMPLE 26

The reaction is carried out as in Example 2 except the catalyst ischarged as 0.067 g. RhH(CO)[P(C₆ H₅)₃ ]₃. Analysis of the productsolution shows the presence of 0.16 g. of methanol and 0.11 g. ofethylene glycol.

EXAMPLE 27

The procedure of Example 25 is repeated using rhodium oxide and rhodiumchloride, respectively, in lieu of elemental rhodium with comparableresults.

EXAMPLE 28

The procedure of Example I is repeated except the solvent isN,N-diethylpropionamide. Analysis of the product shows 0.02 g. methanoland 0.18 g. ethylene glycol.

EXAMPLE 29

The procedure of Example I is repeated except the solvent isN-ethylpyrrolidin-2-one. Analysis of the product shows 0.17 g. methanoland 0.38 g. ethylene glycol.

EXAMPLE 30

The procedure of Example I is repeated except the solvent isN,N-diethyl-m-toluamide. Analysis of the product shows 0.07 g. methanoland 0.17 g. ethylene glycol.

In each of the foregoing examples, the analyses were carried out usinggas-liquid chromatography and in no instance was there any polyol,excepting ethylene glycol, detected.

The amide solvents used in the foregoing examples were freed of aminecontaminants by distillation.

As mentioned hereinbefore, amines appear to show a negative influence onthe yield of glycol and thus are preferably avoided. Accordingly, aminesolvents and amine ligands for the rhodium carbonyl complex are notemployed because of the said negative influence which can result inlittle, if any, yield of the desired ethylene glycol depending on theamount of amine present. Thus, when pyridine is present in the reactionmixture, the yield of ethylene glycol is appreciably diminished, theextent of diminution of yield being proportional to the molar ratio ofpyridine to rhodium; when hydroxypyridine is used as ligand for therhodium carbonyl complex a similar diminution of yield of ethyleneglycol is observed. The following examples illustrates the negativeinfluence of amines on the present process.

EXAMPLE 31

The procedure of Example I is repeated using 0.073 millimole Rh(CO)₂ (C₅H₇ O₂) and 15.8 millimoles paraformaldehyde in 5 ml.N-methylpyrrolidin-2-one which is stirred for 5 hours at 150° C. Theinitial pressure is 5000 psig (H₂ CO=2.2).

Using this procedure, the effect of addition of various levels ofpyridine is determined and the results given in Table I.

                  TABLE I                                                         ______________________________________                                                           % Yield     Productivity                                   Expt.  Pyridine Added                                                                            (Glycol and moles/mole Rh                                  No.    moles/mole Rh                                                                             Methanol)   Glycol Methanol                                ______________________________________                                        1      0           47          70      42                                     2      0.16        67          45     114                                     3      0.3         80          26     163                                     4      1.0         75          11     167                                     ______________________________________                                    

From these data, it is apparent that pyridine exerts a negativeinfluence on the ethylene glycol yield. Similar results are obtainedwith other amines such as methylamine, triethylamine and2-hydroxypyridine.

The effect of hydrogen and carbon monoxide partial pressures, previouslydiscussed herein, is demonstrated by the data of Table II which isdetermined by repeating the procedure of Example 31 without aminepresent but varying the gaseous components.

                  TABLE II                                                        ______________________________________                                               Initial Partial                                                                           % Yield    Productivity                                    Expt.  Pressures, psi                                                                            (Glycol +  Moles/mole Rh                                   No.    H.sub.2 CO      Methanol)                                                                              Glycol Methanol                               ______________________________________                                        1      1410    1900    38       51     30                                     2      2850    1900    45       74     23                                     3      4250    1900    57       93     30                                     4      4250    1055    72       89     68                                     ______________________________________                                    

Variation in reaction temperature provides a somewhat lesser effect,although fairly pronounced, the lower temperatures providing higheryields of ethylene glycol as illustrated in Table III.

                  TABLE III                                                       ______________________________________                                                         % Yield      Productivity                                    Expt.    Temp.   (Glycol and  (moles/mole Rh)                                 No.      °C.                                                                            Methanol)    Glycol                                                                              Methanol                                  ______________________________________                                        1.sup.1  175     37           56    25                                        2.sup.1  150     45           74    23                                        3.sup.1  125     51           74    36                                        4.sup.2  175     47           68    34                                        5.sup.2  150     57           77    46                                        6.sup.3  125     62           98    37                                        ______________________________________                                         .sup.1 5 hrs in 71 ml shaken reactorRh(CO).sub.2 (C.sub.5 H.sub.7             O.sub.2), 0.073 millimole; paraformaldehyde, 15.8 millimoles;                 N--methylpyrrolidinone, 5 ml; H.sub.2 CO, 3:2 at 4760 psi (initial).          .sup.2 3 hrs in 300 ml stirred reactorRh(CO).sub.2 (C.sub.5 H.sub.7           O.sub.2), 1.095 millimole; paraformaldehyde, 237 millimoles,                  N--methylpyrrolidinone, 75 ml; H.sub.2, 3250 psi (initial); CO, 1750 psi      (initial).                                                                    .sup.3 Identical to .sup.2 except 5 hrs.                                 

The following example illustrates the ineffectiveness of rhodiumcarbonyl catalyst in the reaction of carbon monoxide and hydrogen toproduce ethylene glycol and methanol, under the same conditions oftemperature and pressure as employed in the preceding examples.

EXAMPLE 32

Using the procedure of the foregoing examples, except that formaldehydeis omitted, a mixture of Rh(CO)₂ (C₅ H₇ O₂) (0.145 millimoles); ligand(when present) (0.57 millimole) and solvent (5 ml.) is heated at aninitial pressure of 5000 psig (H₂ /CO=1.5) and 200° C. with stirring for10 hours. A series of runs, with and without ligand (2-hydroxypyridineand pyrocatechol) using various solvents including N-methylpyrrolidin-2-one, tetrahydrofuran, tetraglyme and mixtures thereof withmethanol and methyl formate, resulted in no detectable amounts ofethylene glycol and from 0 to 5 millimoles of methanol.

The use of longer or shorter reaction time shows no appreciable changeas is also the case when the catalyst is increased to five times theaforestated amount.

The results are summarized in Table IV.

                                      TABLE IV                                    __________________________________________________________________________    Hydrogenation of CO.sup.(1)                                                                           Ethylene                                              Expt.                   Glycol                                                                              Methanol                                        No. Ligand    Solvent   (Millimole)                                                                         (Millimole)                                                                         Comments                                  __________________________________________________________________________    1   2-Hydroxypyridine                                                                       ThF.sup.(2)                                                                             0     --    .sup.(3)                                  2   "         TG.sup.(4)                                                                              0     1.2                                             3   "         "         0     0.3   .sup.(5)                                  4   "         "         0     3.6   .sup.(6)                                  5   "         TG + HCO.sub.2 CH.sub.3                                                                 0     3.2                                             6   "         TG        0     1.0   .sup.(7)                                  7   Pyrocatechol                                                                            "         0     <0.1  .sup.(7)                                  8   2-Hydroxypyridine                                                                       TG + CH.sub.3 OH                                                                        0     --                                              9   "         TG        0     2.9   .sup.(8)                                  10  "         TG + H.sub.2 C(OCH.sub.3).sub.2                                                         0     5.0                                             11  "         TG        0     0     .sup.(9)                                  12  --        NMP.sup.(10)                                                                            0     0                                               __________________________________________________________________________     .sup.(1) 10 hrs at 200° C. in 71 ml reactors: Rh(CO).sub.2 (C.sub.     H.sub.7 O.sub.2)0.145 millimole; ligand0.57 millimole; Solvent5 ml; 5000      psig initial pressure (H.sub.2 /CO = 1.5)                                     .sup.(2) THF = tetrahydrofuran                                                .sup.(3) Time = 5 hours                                                       .sup.(4) TG = tetraglyme                                                      .sup.(5) No glass liner                                                       .sup.(6) Five times the usual amount of catalyst and ligand                   .sup.(7) 225° C.                                                       .sup.(8) Time = 64 hours                                                      .sup.(9) TG treated with molecular sieves                                     .sup.(10) NMP = N--methylpyrrolidone                                     

EXAMPLE 33

Using the procedure of Example 7 but using paraformaldehyde asformaldehyde source and H₂ /CO=2.1, a variety of N,N-disubstitutedamides are evaluated as solvents with the results summarized in Table V.

                  TABLE V                                                         ______________________________________                                        Solvent           Glycol (g) Methanol (g)                                     ______________________________________                                        N,N--dipropylacetamide                                                                          0.11       0.01                                             N,N--dibutylacetamide                                                                           0.09       0.03                                             N--acetyl piperidine                                                                            0.19       0.31                                             N--propyl pyrrolidine-2-one                                                                     0.11       0.36                                             N--butyl pyrrolidin-2-one                                                                       0.03       0.32                                             N--isopropyl pyrolidin-2-one                                                                    0.17       0.31                                             N--3°butyl pyrolidin-2-one                                                               0.19       0.21                                             ______________________________________                                    

The foregoing examples are illustrative of the combined two stagereaction. Example 34 illustrates the production of glycol aldehyde bythe first state reaction

EXAMPLE 34

The following reaction mixture is charged to a pressure vessel asemployed in the preceding examples:

2.5 mmole Rh (CO)₂ (C₇ H₅ O₂)

237 mmole paraformaldehyde (95%)

5 ml. H₂ O

114 ml. N-methylpyrrolidinone

The vessel is pressured to 2500 psi (P_(co) =2000 psi and P_(H2) =500psi) and then heated to 130° C. and stirred at 1750 rpm. at a constantpressure.

Samples are removed at 15 minute intervals and analyzed with thefollowing results:

    ______________________________________                                        YIELDS (mmoles)                                                               Reaction           Glycol           Ethylene                                  Time (min.)                                                                              CH.sub.2 O                                                                            Aldehyde   MeOH  Glycol                                    ______________________________________                                        15         163     17          0    0                                         30         128     50         19    0                                         45         89      81         29    0                                         60         63      97         34    0                                         75         38      103        45    0                                         90         17      113        59    0                                         ______________________________________                                    

The aldehydes present in the final reaction solution are identified asformaldehyde and glycol aldehyde with no other aldehyde or carboxylcompound being detected. Glycol aldehyde can be separated from thereaction mixture, e.g. by distillation, or the reaction mixture can beused in the second stage reaction as in Example 35. When this procedureis repeated at 160° C., the yield of glycol aldehyde decreasedsubstantially after the first 30 minutes. On repeating this procedure atlower total pressure (P_(co) =2000 psi and P_(H2) =500 psi) slightlylower yield of glycol aldehyde is obtained.

Example 35 illustrates the two stage reaction using the rhodium catalystas the hydrogenation catalyst.

EXAMPLE 35

The procedure of Example 34 is repeated except that the first stage isterminated at the end of one hour and the vessel depressurized bybleeding and then repressurized with hydrogen to 5000 psi so that thehydrogen is 80 mole % of the total gas. The second stage reaction thenproceeds and is sampled at 15 minute intervals for analysis with thefollowing results:

    ______________________________________                                        YIELDS (mmoles)                                                                                      Glycol                                                 Experiment                                                                            Time   H.sub.2 CO                                                                            Aldehyde                                                                             MeOH  Ethylene Glycol                           ______________________________________                                        1       30     131     73     19     0                                                60      64     126    26     0                                                15      6      93     69     10                                               30     <1      43     78     83                                               45     <1      14     73    112                                               60     <1       6     74    117                                       2       30     133     67     19     0                                                60      55     128    26     0                                                15      2      78     69     47                                               30     <2      18     73    115                                               45     <2       6     65    117                                               60     <2       6     62    120                                       3       30     124     70      0     0                                                60      34     150    22     0                                                15     <2      14     64    112                                               30     <2       1     78    127                                               45     <2       6     82    127                                               60     <2       6     79    127                                       ______________________________________                                    

In Experiment 2, 10 ml of glacial acetic acid was added to the reactionmixture before the start of the hydrogenation. In Experiment 3, 20 ml.of H₂ O was added at the beginning of the hydrogenation.

EXAMPLE 36

A pressure vessel is charged with the following: 4 ml. N-methylpyrrolidinone

7.58 mmole formaldehyde (as paraformaldehyde-95%)

0.7 mmole Rh (CO)₂ (C₇ H₅ O₂) and the vessel is pressured to 4000 psiwith CO (80 mole %) and H₂ (20 mole %) and heated at 130° C. for 90minutes.

The product on analysis showed:

1.2 mmole MeOH

0.5 mmole H₂ CO

4.7 mmole glycol aldehyde

The reaction mixture is then pressurized with hydrogen to 75 mole % H₂and 25 mole % and heated at 150° C. for five hours to obtain a productof the following composition:

2.2 mmole MeOH

3.6 mmole ethylene glycol

The reduction step is repeated but with 0.5 g. Ni on kieselguhr and 0.5ml. each of water and acetic acid added to the reaction mixture. Theproduct obtained has the following composition:

1.4 mmole ethylene glycol

1.0 mmole MeOH

and high boiling residue

When this procedure is repeated using Pd/C (5%) in lieu of the Nickelcatalyst, the product has the following composition:

1.8 mmole ethylene glycol

1.7 mmole MeOH

and high boiling residue

When the reduction procedure is repeated but with pure glycol aldehydeusing Pd/C with N-methylpyrolidinone as solvent at hydrogen pressure of3000 psi for 5 hrs. at 150° C. an almost quantitative yield of ethyleneglycol is obtained. Using Nickel on kieselguhr in lieu of Pd/C resultedin lower conversion to ethylene glycol.

The following example shows the results obtained with pure glycolaldehyde in the hydrogenation, as contrasted with Example 36.

EXAMPLE 37

A pressure vessel is charged with the following:

8.3 mmol. glycol aldehyde

4 ml. N-methyl pyrrolidinone

and the selected catalyst system is added. The vessel is thenpressurized to 3000 psi H₂ and heated at 150° C. for five hours toobtain the hydrogenation product with the following results:

    ______________________________________                                                                       Residual                                                                             Ethylene                                                               aldehyde                                                                             glycol                                  Run  Catalyst      Additives   (mmol.)                                                                              (mmol.)                                 ______________________________________                                        1    Rh(CO).sub.2 (C.sub.7 H.sub.5 O.sub.2)                                                      --          0.9    2.4                                          Pd/C (5%)                                                                2    Rh(CO).sub.2 (C.sub.7 H.sub.5 O.sub.2)                                                      50% aq. HOAC                                                                              0.1    7.4                                          Pd/C (5%)                                                                3    Pd/C (5%)     --          0      9.9                                     ______________________________________                                    

The aqueous acetic acid (50%) is present at a level of 20% by volume ofthe reaction mixture.

The results indicate quantitative conversion to ethylene glycol usingPd/C as the sole hydrogenation catalyst. Further, the results with thecombined rhodium and palladium catalysts show that the hydrogenationproceeds substantially better under hydrolytic conditions.

EXAMPLE 38

The following mixture is charged to a pressure vessel as employed in thepreceding examples:

0.004 M/1 Rh catalyst

1.9 M/1 paraformaldehyde (95%)

2.2 M/1 H₂ O

solvent --N-methylpyrrolidinone

The vessel is pressured to 5000 psig (₄ CO:1H₂) and heated to 140° C.with stirring at 1750 rpm with periodic sampling to determine reactionextent. Various catalysts are evaluated using this procedure with thefollowing results:

    __________________________________________________________________________    YIELDS (mmoles)                                                                                             Ethylene                                                                           % HCHO                                              Time (min.)                                                                         HCHO                                                                              HOCH.sub.2 CHO                                                                       MeOH                                                                              Glycol                                                                             Accounted                                  __________________________________________________________________________    Rh(CO)Cl(Ph.sub.3 P).sub.2                                                              5    113  76    14  8    89                                                  10    66  120    16  9    89                                                  15    39  140    17  8    86                                                  30    10  160     9  10   80                                                  60     3  151     9  9    73                                         Rh(CO)H(Ph.sub.3 P).sub.3                                                               5    167  16    11  3    83                                                  10    133  46    19  3    85                                                  15    90   87    18  3    84                                                  30    42  117    34  4    83                                                  60     8  102    32  9    64                                         RhCl(Ph.sub.3 P).sub.3                                                                  5    98   86    13  3    84                                                  10    48  142    13  4    87                                                  15    20  168    15  4    87                                                  30     6  175    13  5    84                                                  60     3  170    15  6    82                                         Rh(CO).sub.2 C.sub.7 H.sub.5 O.sub.2                                                    5    175  0     14  0    77                                                  10    152  15    14  0    76                                                  15    137  30    18  0    78                                                  30    91   53    30  0    82                                                  60    47  103    25  2    75                                         __________________________________________________________________________

From these data it is apparent that those catalysts with the phosphineligand present are more efficient than those without such ligand andfurther that the chloride containing catalysts are most efficient. Inparticular, the chloride-containing rhodium-phosphines provide fastreaction time best yields (70% and higher) and 80-85% selectivity toethylene glycol.

By comparison, the process of U.S. Pat. No. 3,920,753 at best yields 50%yield of glycol aldehyde and a selectivity of only about 50%.

From the experimental data, it is apparent that in the present process ahigh catalyst efficiency is attained as well as a high selectivity toglycol aldehyde in the first stage reaction and to ethylene glycol inthe second stage reaction. In general, the optimum average yield ofglycol aldehyde based on catalyst employed is about 100 moles/mole ofrhodium catalyst. In contrast, in U.S. Pat. No. 3,920,753 the reportedexperimental results show that an optimum of about 14 moles of glycolaldehyde are produced per mole of cobalt catalyst employed.

In addition, it has been found that the reaction product produced inaccordance with the examples of the said U.S. Pat. No. 3,920,753 doesnot readily catalytically reduce to produce appreciable amount ofethylene glycol unless the cobalt catalyst is separated from theproduct. Specifically, the reaction product of Example 4 withoutseparating cobalt catalyst was subjected to various hydrogenationconditions and no significant amount of ethylene glycol was obtained. Inmost cases, no ethylene glycol was detected whereas in a few instancessome glycol was produced but not more than 10% yield based on glycolaldehyde contained in the Example 4 reaction product. In all instances,there was noted a reduction in the glycol aldehyde, indicatingconsumption of the aldehyde apparently forming high-boiling by-products.

Specifically, a comparison of the rhodium-containing reaction product ofthe present invention with the cobalt-containing reaction product ofU.S. Pat. No. 3,920,753 gave the following results:

Hydrogenation conditions: 0.5 g. 5% Pd/C; 30 minutes at 150° C.; 5 ml.H₂ O and 5 ml. of reaction product sample.

    ______________________________________                                                                       Ethylene                                                 gas (psi)  Methanol  Glycol                                         ______________________________________                                        Rh Catalyst,                                                                              (a)    1000 H.sub.2                                                                            28      72                                       4.3 mmole glycol                                                                          (b)    1000 H.sub.2                                                                            25      >100                                     aldehyde           4000 CO                                                    Co Catalyst (a)    1000 H.sub.2                                                                            18      0                                        4.9 mmole glycol                                                                          (b)    1000 H.sub.2                                                                             6      6                                        aldehyde           4000 CO                                                    ______________________________________                                    

The resulting products were analyzed for carbonyl, i.e., glycolaldehyde, and the Rh-catalyst containing products showed, respectively,1% and 0%, whereas the C-catalyst containing products showed 53% and15%, respectively.

What is claimed is:
 1. A process which comprises reacting formaldehyde,carbon monoxide and hydrogen in an aprotic solvent at a temperature offrom about 75° C. to about 250° C. and superatmospheric pressure up toabout 700 atmospheres to form glycol aldehyde in a first reaction stageand subsequently catalytically reducing the glycol aldehyde to formethylene glycol in a second reaction stage, wherein a catalytic amountof rhodium in complex combination with carbon monoxide is present atleast during said first reaction stage.
 2. A process according to claim1 wherein said rhodium is present during said second reaction stage. 3.A process according to claim 1 wherein a hydrogenation catalyst ispresent during said second stage reaction.
 4. A process according toclaim 3 wherein said rhodium is removed from the first reaction stageproduct prior to said second stage reaction.
 5. A process according toclaim 3 wherein said hydrogenation catalyst comprises palladium.
 6. Aprocess according to claim 1 wherein said first and second stagereactions are conducted at a temperature of from about 100° to about175° C.
 7. A process for producing glycol aldehyde and/or.[.ethyleneblycol.]. .Iadd.ethyleneglycol .Iaddend.which comprisesreacting formaldehyde, carbon monoxide and hydrogen in an aproticsolvent at a temperature of from about 75° to about 250° C. and apressure of from about 10 to about 700 atmospheres in the presence of acatalytic amount of a catalyst comprised of rhodium in complexcombination with carbon monoxide and recovering glycol aldehyde and/orethyleneblycol from said reaction.
 8. A process according to claim 7wherein said catalyst further comprises a tri-organo phosphine ligand.9. A process according to claim 7 wherein said catalyst furthercomprises a triaryl phosphine ligand.
 10. A process according to claim 7wherein said temperature is in the range of from about 100° to about175° C. and said pressure is in the range of from about 150 to about 400atmospheres.
 11. A process according to claim 10 wherein the molar ratioof hydrogen to carbon monoxide is from about 1/10 to about 10/1.
 12. Aprocess according to claim 10 wherein the reaction is carried out in thepresence of a solvent comprising an aprotic organic amide.
 13. A processaccording to claim 12 wherein the solvent comprises an N-lower alkylpyrrolidin-2-one.
 14. A process according to claim 12 wherein thesolvent comprises an N,N-di(lower alkyl)acetamide.
 15. A processaccording to claim 12 wherein the solvent comprises N-methylpyrrolidin-2-one.
 16. A process according to claim 12 wherein thesolvent comprises N,N-diethyl acetamide.
 17. A process according toclaim 12 wherein the solvent comprises N,N-diethyl propionamide.
 18. Aprocess of producing ethylene glycol which comprises the steps of: (A)reacting formaldehyde, carbon monoxide and hydrogen in an aproticsolvent at a temperature of from about 75° to about 250° C. andsuperatmospheric pressure up to about 700 atmospheres in the presence ofa catalytic amount of a catalyst comprised of rhodium in complexcombination with carbon monoxide to form glycol aldehyde; and (B)catalytically hydrogenating said glycol aldehyde under hydrolyticconditions to produce ethylene glycol.
 19. A process according to claim18 wherein the solvent comprises an N-lower alkyl pyrrolidin-2-one. 20.A process according to claim 18 wherein the solvent comprises N-methylpyrrolidin-2-one.
 21. A process according to claim 18 wherein thetemperature is from about 100° to about 175° C. and the pressure is fromabout 150 to about 400 atmospheres.
 22. A process according to claim 18wherein the catalyst for said catalytic hydrogenation comprisespalladium or rhodium.
 23. A process according to claim 18 wherein saidhydrogenating is carried out in the presence of aqueous acid.
 24. Aprocess according to claim 23 wherein said acid is acetic acid. .Iadd.25. A process for producing ethylene glycol which comprises reactingformaldehyde, carbon monoxide and hydrogen in an aprotic solvent at atemperature of from about 75° to about 250° C. and a pressure of fromabout 10 to about 700 atmospheres in the presence of a catalytic amountof a catalyst comprised of rhodium in complex combination with carbonmonoxide and recovering ethylene glycol from said reaction. .Iaddend..Iadd.26. A process according to claim 25 wherein said catalyst furthercomprises a tri-organo phosphine ligand. .Iaddend. .Iadd.27. A processaccording to claim 25 wherein said catalyst further comprises a triarylphosphine ligand. .Iaddend. .Iadd.28. A process according to claim 25wherein said temperature is in the range of from about 100° to about175° C. and said pressure is in the range of from about 150 to about 400atmospheres. .Iaddend. .Iadd.29. A process according to claim 28 whereinthe molar ratio of hydrogen to carbon monoxide is from about 1/10 toabout 10/1. .Iaddend. .Iadd.30. A process according to claim 28 whereinthe reaction is carried out in the presence of a solvent comprising anaprotic organic amide. .Iaddend. .Iadd.31. A process according to claim30 wherein the solvent comprises an N-lower alkyl pyrrolidin-2-one..Iaddend. .Iadd.32. A process according to claim 30 wherein the solventcomprises an N,N-di(lower alkyl)acetamide. .Iaddend. .Iadd.33. A processaccording to claim 30 wherein the solvent comprises N-methylpyrrolidin-2-one. .Iaddend. .Iadd.34. A process according to claim 30wherein the solvent comprises N,N-diethyl acetamide. .Iaddend. .Iadd.35.A process according to claim 30 wherein the solvent comprisesN,N-diethyl propionamide. .Iaddend.